FINAL REPORT Monitoring secretive marsh birds in Everglades National Park: a pilot study

Transcription

1 FINAL REPORT Monitoring secretive marsh birds in Everglades National Park: a pilot study COOPERATIVE AGREEMENT: P13AC00021 PROJECT DIRECTOR: Principal Investigator: Gary L. Slater PROJECT PERSONNEL: Wildlife Biologist: Jeannette Parker DATE REPORT SUBMITTED: 18 May 2015 Ecostudies Institute committed to ecological research and conservation

2 INTRODUCTION Emergent wetland ecosystems have been severely impacted across North America, perhaps no place more severely than in the Everglades of Florida. Drainage for agriculture and complex engineering for flood control and water storage have compartmentalized the wetland system markedly altering natural water flows and flood cycles. Although much of the physical alterations to this system (ditches, levees, impoundments) have occurred outside of Everglades National Park (ENP), wetland ecosystem function within ENP has been greatly diminished due to its downstream position. Large scale restoration efforts (e.g., CERP) have been undertaken to restore more natural hydrological patterns in the Everglades region and improve wetland function. The loss and degradation of wetlands has had a significant impact on wildlife. For example, some wading bird populations have declined by 90% and several populations of the endangered Cape Sable Seaside Sparrow have nearly disappeared (DOI 2005, Pimm et al. 2002). In contrast, many novel exotic species, such as the Burmese Python (Python molurus) and exotic apple snails (e.g., Pomacea insularum) have apparently flourished (Snow et al. 2007, Rawlings et al. 2007). Secretive marsh birds are among the most inconspicuous group of birds in North America, in part, because they inhabit emergent wetlands characterized by dense vegetation and they vocalize infrequently. This group of birds has never been adequately surveyed by any previous sampling effort in ENP. Like other wildlife, they undoubtedly have been impacted by wetland alteration. They also appear vulnerable to new threats, most notably through direct predation by pythons (Dove et al. 2011). Rails and their allies, which comprise the majority of marsh bird diversity, are consumed by pythons more than any other avian taxa. Throughout history, ground-dwelling marsh birds have been particularly vulnerable to extinction on islands, mainly from introduced predators. Limpkins (Aramus guarauna), a USFWS species of concern (USFWS 2008), may also be impacted by the expanding distribution of exotic apple snails, which compete with the native apple snail, the limpkins primary food source (Bryan 2001). Without a better understanding of the abundance of secretive marsh birds, their distribution, or their life history in the region, it is impossible to assess their population status, Page 2

3 predict the effect of management (e.g., restoration), or evaluate the impact of exotic species. We addressed this problem through a pilot investigation of secretive marsh birds during the 2013 breeding season in ENP. Using the recently established standardized monitoring protocol for marsh birds (Conway 2011), we surveyed sites across ENP to determine marsh bird abundance and distribution on across ENP. The primary objectives associated with this research were to: 1) establish survey routes for monitoring marsh birds in ENP, 2) estimate the abundance and distribution of marsh birds in ENP, and 3) develop a long-term monitoring protocol for marsh birds in ENP. METHODS Study Area The study area was located in ENP, a U.S. National Park and World Heritage site that covers 1.5 million acres throughout Dade, Monroe, and Collier counties in Florida. ENP includes a wider array of habitats including forested uplands, a diverse mosaic of freshwater wetlands, and coastal wetlands and mangrove forests that transition into the open water marine ecosystems of the Gulf of Mexico and Florida Bay. Much of the park is classified as wilderness. In this study, we restricted our surveys in ENP to seasonally flooded freshwater and coastal marshes that were readily accessible by road or foot. Establishing survey route Survey routes were a permanent grouping of points that were surveyed together. The number of points per survey route varied among routes based on the availability of suitable wetland habitat and the number of points that one surveyor could survey during a sampling event (a morning or evening). We established survey routes with the goal of covering as much variation in possible with respect to habitat type, hydrology, and salinity. We met with ENP Park biologists to discuss route placement, and it was generally agreed that groups of 2-3 routes should be placed around the Coastal Prairie Trail, Main Park Road, Old Ingraham Highway, Eastern boundary of ENP (North and South) and Shark Valley (including the L67 levee). Focusing on these areas will provide wide coverage across the park and also ensure the main habitat types and conditions Page 3

4 are covered. Preliminary field visits indicated access to these areas was feasible and habitat was appropriate for surveys. We established survey routes following the Standardized North American Marsh Bird Monitoring Protocol (Conway 2011). Survey routes were > 1 km apart (most were >3.5 km apart). Points were spaced 400 m apart. Overall, we established 103 points on 12 survey routes across ENP (Table 1, Figure 1). Except for Shark Valley and Coastal Prairie Trail, routes were accessed by automobile; Shark Valley was surveyed by bicycle or on foot and the Coastal Prairie Trail was surveyed on foot. Table 1. List of survey routes, number of points, how route was surveyed, and direction that playback faced for marsh bird surveys conducted during the 2013 breeding season in Everglades National Park, FL. Survey Route Name Number of Points Accessed Playback Faced Shark Valley 10 Walk/Bicycle East Levee 67 North 8 Vehicle East Levee 67 South 9 Vehicle East Levee 31 North 8 Vehicle West Context Road 9 Vehicle/Walk West; CTR2-south, CTR3 - north Levee 31 West 9 Vehicle West Main Park Road Taylor Slough 8 Vehicle North Old Ingraham Hwy East 10 Vehicle East Old Ingraham Hwy 10 Vehicle South Pahayokee 6 Vehicle East Main Park Road 9 Vehicle East Coastal Prairie Trail 7 Walk/Trail North Page 4

5 Figure 1. Map of survey route locations (upper left), with detailed route names and location of points in North EVER (upper right), East central EVER (bottom right) and South EVER (lower left). Page 5

6 Survey methods We followed the survey methods described in the Standardized North American Marsh Bird Monitoring Protocol (Conway 2011). We surveyed routes during five, 2-week survey periods from 1 May to 15 July. We initially planned to survey for only four periods, but because marsh birds were still active and yielding detections, particularly of species not recorded in earlier sampling periods, we added an additional survey period. In South Florida, the recommended survey period is three 2-week periods from 1 April -15 May (Conway 2011). However, Conway et al. (2010) found that the recommended survey period may be too short and peak detection periods for common species coincided with an increase in water depth caused by summer rains. We surveyed each route by foot, bicycle, or vehicle during the morning (0.5 hours before sunrise until 2 hours after sunrise) or the evening (2 hours before sunset until 0.5 hours after sunset. We surveyed each survey point on a route in the same chronological order during each repeated visit. We did not survey during periods of inclement weather (high winds or prolonged and heavy rain). At each survey point along a route, we conducted a 10 minute survey, broken down into a 5-minute passive listening period and a 5-minute call-broadcast period. We recorded all aural and visual detections. During the 5-minute playback, we played a 30 sec vocalization clip followed by 30 sec of silence. The five species that we included in the call-broadcast component were, in the following order: Least Bittern (Ixobrychus exilis), King Rail (Rallus elegans), Purple Gallinule (Porphyrio martinica), Common Moorhen (Gallinula chloropus), and Limpkin. The order of call-broadcasts was by ascending level of presumed intrusiveness. In tidal, or brackish, wetlands we replaced King Rail with Clapper Rail (Rallus longirostris). The survey was divided into 10 1-min segments and we recorded when the initial detection of the species occurred during the survey and subsequent detections in subsequent 1-minute intervals. Water Depth We estimated water depth along each survey route using the Everglades Depth Estimation Network (EDEN). Using the EDEN xylocator app, we determined water depth at each survey point on every day a survey was conducted. We averaged water depth among individual survey Page 6

7 points for each route, yielding a single water depth value for every survey conducted along a route. Data Summary We estimated average species abundance and total abundance by point for each survey period and each route to examine patterns of abundance and distribution. For this pilot study, we did not correct abundance estimates by detectability. However, we evaluated the effect of the call broadcast on increasing detections. We calculated the proportion of birds detected during each 1-minute survey segment for each species using the following ratio: RESULTS Number of individuals detected during 1-minute segment Total number of detections We surveyed a total of 510 points along 12 routes across freshwater and coastal wetlands in ENP over 5, 2-week survey periods from 1 May to 15 July Overall, we detected 322 individuals consisting of 136 King Rails, 59 Purple Gallinules, 58 Pied-billed Grebes, 26 Limpkins, 28 Least Bitterns, 8 Clapper Rails, and 7 Common Moorhens. Marsh birds were most abundant on the Context Road route (0.83 birds/pt., SD = 0.38), followed by L67 south (0.72, SD = 0.45), Pahayokee (0.60, SD = 0.49) and L67 North (0.57, SD = 0.50); Coastal Prairie Trail only had Clapper Rails detected along the route and had the lowest average number of marsh birds detected (0.21, SD = 0.41; Table 2). Marsh bird abundance was highest in June, during rounds 3 and 4, and lowest in late May (Round 2; Table 2). King Rail and Clapper Rails were the most abundant marsh bird, with mean abundance (SD) per point of 0.28 (0.69) and 0.23 (0.64) respectively. They also were more likely to be detected in the earlier survey rounds than later in the season (Table 3). The remaining 6 species were less abundant with mean abundance for Pied-billed Grebes was 0.11 (0.52), followed by Purple Gallinule (0.11, SD = 0.50), Limpkin (0.05, SD = 0.28), Least Bittern (0.05, SD = 0.24), Common Moorhen (0.01, SD = 0.11). Several species, including Least Bittern, Pied-billed Grebe, and Clapper Rail were not detected until the 3 rd round of surveys, which began on 1 June (Table 3). Page 7

8 Table 2. Mean (SD) total abundance of secretive marsh birds by point, survey round, and survey route during the 2013 breeding season in Everglades National Park, FL. Round Route n Total abundance n = st (1 May -15 May) (0.50) 2 nd (16 May 30 May) (0.46) 3 rd (1 June 15 June) (0.50) 4 th (16 June 30 June) (0.49) 5 th (1 July 15 July) (0.50) Coastal Prairie Trail (0.41) Context Road (0.38) L31 North (0.48) L31 West (0.50) L67 North (0.50) L67 South (0.45) Main Park Road (0.42) Old Ingraham Hwy (0.46) Old Ingraham Hwy East (0.33) Pahayokee (0.49) Shark Valley (0.50) Taylor Slough (0.46) In general, species abundance varied by survey route (Table 3). King Rails, Limpkins, and Purple Gallinule had their highest abundance on Context Road, while Common Moorhen, Least Bittern, and Pied-billed Grebe had their highest abundance on Pahayokee (Table 3). Water depth on routes increased over the summer as expected with the onset of the rainy season (Table 4). Overall, we did not see a relationship with bird abundance and water depth (R 2 = 0.007), even when several large counts were removed (R 2 = 0.073; Figure 2). Even when individual species were examined, there appears to be little relationship (Figure 3). The largest number of detections for all species was in the 1-minute segment when the call broadcast was played, indicating detection probability increased when call-broadcast was used (Figure 4). Page 8

9 Table 3. Mean species abundance of marsh birds by survey round and survey route during the 2013 breeding season in Everglades National Park, FL. Round Route Common Least Pied-billed Purple Limpkin King Rail Clapper Rail Moorhen Bittern Grebe Gallinule n n = 7 n = 28 n = 7 n = 58 n = 59 n = 136 n = 8 1 st (1 May -15 May) (0.10) (0.31) (0.22) 0.49 (0.92) nd (16 May 30 May) (0.20) (0.28) 0.31 (0.65) rd (1 June 15 June) (0.20) 0.05 (0.22) 0.09 (0.32) 0.12 (0.41) 0.17 (0.47) 0.25 (0.64) 0.29 (0.49) 4 th (16 June 30 June) (0.32) 0.07 (0.32) 0.29 (0.83) 0.22 (0.79) 0.23 (0.57) 0.43 (1.13) 5 th (1 July 15 July) (0.14) 0.11 (0.34) 0.04 (0.24) 0.16 (0.69) 0.13 (0.52) 0.15 (0.58) 0.43 (0.79) Coastal Prairie Trail ** ** 0.23 (0.65) Context Road (0.62) 0.58 (1.20) 0.69 (1.20) 0.69 (1.06) ** ** L31 North (0.16) 0.05 (0.32) 0.20 (0.72) 0.03 (0.16) 0.10 (0.30) ** ** L31 West (0.15) 0.09 (0.36) 0.18 (0.53) (0.33) 0.18 (0.58) ** ** L67 North (0.27) (0.86) ** ** L67 South (0.15) 0.20 (0.40) (0.34) 0.31 (0.76) 0.42 (0.89) ** ** Main Park Road (0.21) (0.21) (0.40) ** ** Old Ingraham Hwy (0.75) ** ** Old Ingraham Hwy East (0.14) (0.14) (0.31) 0.02 (0.14) ** ** Pahayokee (0.31) 0.10 (0.31) 0.03 (0.18) 0.47 (1.01) 0.10 (0.31) 0.07 (0.25) ** ** Shark Valley (0.29) 0.02 (0.15) (0.36) 0.36 (0.83) ** ** Taylor Slough (0.16) 0.05 (0.22) 0.03 (0.16) 0.05 (0.22) (0.36) ** ** Page 9

10 Table 4. Average water depth (cm) along survey routes during breeding season marsh bird surveys in 2013 in Everglades National Park. The EDEN network does not cover the area where our Coastal Prairie Trail route was placed (NA = Not available). Coastal Prairie Trail Water Water Round Main Park Road Round depth depth 1 NA NA NA NA NA Context Road Old Ingraham Hwy L31 North Old Ingraham Hwy East L31 West Pahayokee L67 North Shark Valley L67 South Taylor Slough Page 10

11 Figure 2. Relationship between bird abundance and average water depth on survey routes conducted during the 2013 breeding season in Everglades National Park. Upper figure shows all data (n= 55), while the lower figure shows data with the three largest counts removed (n = 52). Data from the Coastal Prairie Trail are not included because water depth data were not available. Page 11

12 Figure 3. Relationship between King Rail (upper), Pied-billed Grebe (middle) and Purple Gallinule (lower) abundance and average water depth on survey routes conducted during the 2013 breeding season in Everglades National Park. Data from the Coastal Prairie Trail are not included because water depth data were not available. Page 12

13 Figure 4. The percentage of total detections among 1-minute segments of marsh bird surveys conducted during the 2013 breeding season in Everglades National Park, FL for Common Moorhen, Clapper Rail, King Rail, Least Bittern, Pied-billed Grebe, Limpkin, and Purple Gallinule. Red bar indicates the 1-minute segment when that species call-broadcast was played. Page 13

14 DISCUSSION In this pilot study, we provide the first description of the abundance and distribution of marsh birds in Everglades National Park. Many of the observations gained in this pilot study, particularly related to the timing of surveys and the use of call-broadcast playbacks, are helpful for considering a more comprehensive and longer-term effort. While the marsh bird community is not diverse during the breeding season in this region, we found that some species were relatively abundant, and thus offer the potential to serve as an attribute to evaluate effects of management, including restoration. We found that the number of birds detected varied substantially among our 5, 2-week survey periods. King and Clapper Rails were most abundant in the first two survey periods, which occurred prior to the onset of the summer rains and declined thereafter. In general, habitat conditions were relatively dry when these species were detected, as evidenced by the lower water depths at routes in those periods. Other species, such as Purple Gallinules, Least Bitterns, and Pied-billed Grebes were not detected until the 3 rd, 2-week period. At that time the rainy season was in full swing and marshes were becoming wetter. The standardized marsh bird protocol recommends 3, 2-week survey periods from 1 April 15 May in south Florida (Conway 2011). Due to late funding, we were unable to start surveys until 1 May, nearly missing most of the recommended survey. However, it is clear that for some species, the recommended survey period for South Florida is too early. Indeed, Conway et al. (2013) found a similar result when conducting surveys in southwest Florida. Any plan to initiate a long-term monitoring effort will need to cover the period from the late dry season to well into the rainy season. Although surveys need to cover a long enough period to encompass the breeding season, which overlaps the rainy season, exploratory analysis of our pilot data indicated that marsh bird abundance was not correlated with water depths. We did not measure water depth at individual sites; rather we relied on water depth coverages generated by EDEN. EDEN generates water depth maps at 400 x 400 meter cells, and this may be too coarse of a scale for the purpose used in this exercise. If additional marsh bird monitoring is conducted in the future, we recommend collecting water depth data at each route. Page 14

15 Marsh birds are known for their secretive behavior, inhabiting wetlands with dense vegetation and rarely vocalizing. These characteristics make them a challenge to monitor. However, the standardized protocol implements a call-broadcast method to increase detectability. Like many other authors, we found that playbacks greatly increased detectability. For all five species, we found the greatest number of detections in the 1-minute segment when that species call-broadcast was played. We did not specifically estimate detectability for individual species and recommend that be conducted with these pilot data to fully evaluate the impact of call-playback on detectability. Overall, the pilot study provides a window of information about the marsh bird community, offering a potential springboard for additional study. With information about marsh bird abundance and detectability from this study, there is the ability to conduct a power analysis to evaluate the ability to detect long-term trends in abundance as part of a long-term monitoring program. We recommend a power analysis as an important next step in the study of this unique avian taxa. Further, there also is the opportunity to further explore avian-habitat relationship. Finally, we also recommend that future work consider investigating patterns of marsh bird abundance and habitat use in the non-breeding season, a time when marsh bird diversity is substantially higher than in the breeding season. REFERENCES Bryan, D.C Limpkin (Aramus guarauna), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: (Accessed 5/18/2012). Conway, M. A., C. P. Nadeau, and C. J. Conway Optimal seasonal timing of marsh bird surveys and the effect of water quality on relative abundance of marsh birds in south Florida. Wildlife Report # USGS Arizona Cooperative Fish and Wildlife Research Unit, Tucson, Arizona. Conway, C. J Standardized North American marsh bird monitoring protocol. Waterbirds 34: Page 15

16 Dove, C. J., R. W. Snow, M. R. Rochford, and F. J. Mazzotti Birds consumed by the invasive Burmese Python (Python molurus bivittatus). Wilson Journal of Ornithology 123: Pimm, S. L., J. L. Lockwood, C. N. Jenkins, J. L. Curnutt, M. P. Nott, R. D. Powell, and O. L. Bass, Jr Sparrow in the grass. A report on the first ten years of research on the Cape Sable seaside sparrow (Ammodramus maritimus mirabilis). Everglades National Park Service, Homestead, Florida, USA. Rawlings, T.A., K.A. Hayes, R.H. Cowie, and T.M. Collins The identity, distribution, and impacts of non-native apple snails in the continental United States. BMC Evolutionary Biology, Volume 7, No. 97. Snow, R.W., K. L. Krysko, K.M. Enge, L.Oberhofer, A. Warren-Bradley, and L.Wilkins Introduced populations of Boa constrictor (Boidae) and python Molurus bivittatus (Pythonidae) in southern Florida. Pages in Biology of the boas and pythons (R. W. Henderson and R. Powell, Editors). Eagle Mountain Publishing, Eagle Mountain, Utah, USA. U. S. Fish and Wildlife Service [USFWS] Birds of conservation concern 2008 United States Department of Interior, Fish and Wildlife Service, Division of Migratory Bird Management, Arlington, VA. Page 16